A Muslim who from the family (tree) of Prophet Muhammad cannot accept Zakah, but can his wife who is not from the Prophet's family accept Zakah? If so, can she give it to her husband as a gift or as charity (Sadaqa)?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

There is no harm for the descendants of the Prophet (Sallallahu Alaihi wa Sallam) to accept a gift even if the person offering it has acquired it as a Sadaqah.  The evidence about this is in Saheeh Muslim and Bukhari that Anas (Radiya Allahu Anhu) narrated that the Prophet (Sallallahu Alaihi wa Sallam) brought some meat which was given as Sadaqah to Barira, and he said: "For her it is considered a Sadaqah, and for us it is considered a gift".

What is concluded from the Hadith, as in Fath al-Bari, is that a descendant of the family of the Prophet (Sallallahu Alaihi wa Sallam) can accept a gift which is originally a Sadaqah.

However, it is not acceptable for him to accept a Sadaqah from his wife because the descendants of the family of the Prophet (Sallallahu Alaihi wa Sallam) are not allowed to take Sadaqah.

Muslim reported that Abu Hurairah (Radiya Allahu Anhu) narrated: "Hassan bin Ali took a date from the dates which were given as a Sadaqah and put it in his mouth.’  The Prophet (Sallallahu Alaihi wa Sallam) told him: “Stop, stop, throw it away, did you not know that we are not allowed to take Sadaqah."

We must know that a wife who is sufficiently provided by the husband, is not poor or destitute therefore she is not allowed to be given from the Zakah.

Allah knows best.